Fix all Cortex-M3/4 implementations of up_disable_irq().  They were doing nothing.  Thanks to Manuel Stühn for the tip.

FAT: Fix some root directory logic that was conditionally done only for FAT32.  Apparently this needs to be done for all FAT types.  From Tridge via Lorenz Meier

If write buffering is enabled, then it is necessary to release the write buffer resources (callback structure) when the socket is closed

Add support for the SO_LINGER socket option.  Based on logic from Jason Jiang.  Utestested on initial commit

NSH: Separate command line parsing from command execution.  Add support for multiple, semicolone separated commands on each line

Fix STM32F103VE SPI3 definitions; Fix bug introduced in recent NX reorganization.  From Steve Redler IV